Writing instruments of the respective structures (refer to, for example, patent documents 1 to 5 filed by the present applicant) have so far been known as writing instruments in which a writing direction can be visually recognized at a visual part of a pen tip. Among the above respective patent documents, known as a technique close to that of the present invention is, for example, a writing instrument 1 (refer to, for example, the patent document 1 filed by the present applicant) comprising, as shown in FIG. 25, a pen body 1b which guides an ink supplied from a writing instrument main body 1a and which can reserve it, wherein the pen body 1b described above is equipped with an ink guiding part 1c and a writing part 1d for delivering the ink from the above ink guiding part 1c, and it is equipped as well with a visible part 1e in which a writing direction can be visually recognized right above a holder direction of the above writing part 1d. In particular, the respective pen bodies shown in FIG. 26 and FIG. 27 disclose techniques closest to that of the present invention.
FIGS. 26 (a) and (b) are drawings of the sixth embodiment of a pen body in the writing instrument described in patent document 1 described above. The pen body 2 of the above embodiment is endowed with a structure in which a writing part 2c fixed by a leg part 2b is provided at a front end of a transparent supporting member 2a and in which provided is an ink guiding part 2d comprising an ink guiding groove communicating with a rear end of the leg part 2b in the above writing part 2c and enabling to guide the ink to a prescribed part in an inside of the supporting member 2a described above by a capillary action. Since the supporting member 2a is constituted by a transparent resin and the like, a part 2e becomes a visible part, and a writing direction is visually recognized through an ink flowing in an inside of the supporting member 2a. 
Also, FIGS. 27 (a) and (b) show the eighth embodiment of a pen body in the writing instrument described in patent document 1 described above. The pen body 3 of the above embodiment has almost the same structure as that of the pen body of the sixth embodiment in FIG. 26 described above, and a different point thereof resides in a structure in which a window part 3b as a visible part is provided in a supporting member 3a, in which an ink guiding groove 3c is formed bypassing the above window part 3b and in which an ink can be fed to a writing part 3d by a capillary action.
However, in the writing instrument described in patent document 1 described above, taken is a structure in which the ink guiding parts 1c, 3c are provided at both sides of the visible parts 1e, 3b in FIG. 25 and FIG. 27 and in which the writing parts 1d, 3d are provided at a lower part thereof, and therefore an area ratio of the visible part 1e having visibility is actually a level of 30% of the pen tip (pen body) protruding from a tip part of the writing instrument main body. Accordingly, a problem is involved in the point that the satisfactory visibility can not be secured and that it is a little difficult to see the writing direction. If the visible part is enlarged, visibility in the writing direction is broadened, but the writing part is enlarged as well, so that the writing performances as a line marker are damaged.
Also, in the pen body 2 shown in FIG. 26, a writing direction is visually recognized through an ink flowing through an inside of the supporting member 2a, and therefore a problem is involved in the point that it is difficult to see the writing direction when the ink has a deep color. Further, the leg part 2b fixed in an inside of the supporting member 2a does not have visibility, and therefore an area ratio of the visible part having visibility is actually a level of 30% of the pen tip (pen body) protruding from a tip part of the writing instrument main body. Accordingly, the satisfactory visibility can not be secured, and the existing situation is that a pen body having a structure in which a writing direction can further widely be visually recognized is desired.
On the other hand, known as a writing instrument of an ink exhaustion detecting system in which a part of a writing direction in a back of the writing part can be visually recognized and in which an exhaustion sign of an ink can be detected are, for example, a writing instrument 4 of an ink exhaustion detecting system in which as shown in FIGS. 28 (a) and (b), an ink impregnated in an ink occulusion body 4b in an inside of a barrel 4a is fed to a pen tip 4e of a writing part via a feed 4c and an ink guiding part 4d and in which an exhaustion sign of the ink in the ink occulusion body 4b is visually recognized in the ink guiding part 4d described above to thereby detect it, wherein the ink guiding part 4d described above comprises a visible part 4f capable of visually recognizing a writing direction and an ink guiding tube 4g at a side part of the above visible part 4f (refer to, for example, patent document 6 filed by the present applicant) and a writing instrument 5 of an ink exhaustion detecting system in which as shown in FIGS. 29 (a) and (b), an ink impregnated in an ink occulusion body 5b in an inside of a barrel 5a is fed to a pen tip 5e as a writing part via a feed 5c and an ink guiding part 5d and in which an exhaustion sign of the ink in the ink occulusion body 5b is visually recognized in the ink guiding part 5d described above to thereby detect it, wherein the ink guiding part 5d described above comprises a tabular ink guiding part 5g provided with a slit ink passage 5f having a thickness of 0.01 to 1.0 mm in an inside thereof; a visible light transmittance of the ink guiding part 5g in filling the ink is 50% or more; and a writing direction directly under an axis direction of the above ink guiding part 5g can be visually recognized via the ink guiding part 5g (refer to, for example, patent document 7 filed by the present applicant).
However, in the writing instrument 4 shown in FIGS. 28 (a) and (b), the ink guiding tube 4g is thickened (enlarged) in order to surely detect the exhaustion sign, and therefore a little problem is involved in the point that the sufficiently high visibility can not be secured. Further, the existing situation is that, it is not easy to secure a sealing property of the pen tip and obtain a structure in which the ink is exhausted to the end, due to a complicated shape of the ink guiding tube 4g. 
Also, in the writing instrument 5 shown in FIGS. 29 (a) and (b), if the ink guiding part is reduced in a thickness to such an extent that the sufficiently high visibility can be secured, the ink flow amount can not be secured. On the other hand, if the ink flow amount is intended to be secured, the sufficiently high visibility can not be secured, and therefore the effective visible part is limited to make it difficult to secure the visibility.    Patent document 1: Japanese Patent Application Laid-Open No. 52682/2000 (claims, embodiments, FIG. 1, FIG. 11, FIG. 12 and others)    Patent document 2: Japanese Patent Application Laid-Open No. 253193/2001 (claims, embodiments, FIG. 1 and others)    Patent document 3: Japanese Patent Application Laid-Open No. 19370/2002 (claims, embodiments, FIG. 1 and others)    Patent document 4: Japanese Patent Application Laid-Open No. 246606/2005 (claims, embodiments, FIG. 1 and others)    Patent document 5: Japanese Patent Application Laid-Open No. 256045/2006 (claims, embodiments, FIG. 1 and others)    Patent document 6: Japanese Patent Application Laid-Open No. 69426/2007 (claims, embodiments, FIG. 1 and others)    Patent document 7: Japanese Patent Application Laid-Open No. 69427/2007 (claims, embodiments, FIG. 1 and others)